The present invention relates to thermally regenerated, reciprocating, two stroke external combustion engines that store the exhaust heat and return it to the engine cycle to do work.
Thermal regeneration is the capturing of waste heat from a thermodynamic cycle (or a heat engine operating on some thermodynamic cycle), and the utilization of that energy within the cycle or engine to improve the cycle or engine""s performance. This is commonly done with many heat engines including Stirling engines, gas turbines, and Rankine cycle devices. In a gas turbine the exhaust heat coming out of the exhaust is transferred to the fluid leaving the compressor and going into the combustor. This way it is not necessary to add as much heat (fuel) in the combustor to raise the fluid temperature to the desired turbine inlet temperature. This means that the same work is accomplished but less fuel is used. The approach taken by most inventors who attempted to incorporate regeneration into reciprocating external combustion engines was to try to regenerate existing designs. The three most successful designs are: the four cycle Otto cycle, the two stroke gasoline engine, and the so called twin cylinder engines where the air is compressed in one chamber, combusted in another, and expanded in a third. With the exception of Clark (1996, U.S. Pat. No. 5,540,191) all of the existing designs are four cycle designs with adaptation to two stroke engines such as Wakeman (1981, U.S. Pat. No. 4,284,055); Ferrenberg and Webber (1988, U.S. Pat. No. 4,790,284) and (1990, U.S. Pat. No. 4,928,658); and Ferrenberg (1995, U.S. Pat. No. 5,465,702) and (1997, U.S. Pat. No. 5,632,255). The major drawback to all of the above two stroke designs is that they improve existing designs (crankcase compression or the use of external compression) instead of using the regenerator to aid in the intake and exhausting of air and products of combustion. With crankcase compression engines, no scavenging of the cylinder is possible, the volumetric efficiency is low (30 to 50 percent), and the engine is limited to operation at low piston speed (usually less than 1,000 fpm) for economical operation. Other differences exist between the engines and the regenerated engine disclosed herein. All of these are discussed in greater detail in the section entitled xe2x80x9cDetailed Description of the Inventionxe2x80x9d.
This invention is a two stroke, regenerated, external combustion, reciprocating engine made up of a number of similar working units. Each working unit is comprised of a cylinder that is closed at one end by a cylinder head and contains a movable power piston that is connected to a power output shaft. Means are provided (a plunger) to suck in the fluid and push the exhaust out of the cylinder. This plunger can move between the power piston and the cylinder head, and means are provided to accomplish this movement at the appropriate times during the engine""s operating cycle. The plunger is a movable wall that has attached to it a plunger valve which opens to allow fluid to flow through the movable wall while the plunger is moving away from the piston, and closes to form a suction plunger while the plunger is moving towards the piston. The plunger also has attached to it an exhaust pipe, an exhaust valve that opens while the plunger is moving towards the power piston, a heater, and an alternating flow heat exchanger, called a regenerator. The movement of the plunger with its regenerator is such that the regenerative exhaust cooling stroke (the regenerator is heating) begins when the power piston is at about 85% of the way from the cylinder head, and ends when the power piston is about 15% of the way towards the cylinder head. The compressed fluid heating stroke (the regenerator is giving up heat) begins at about 85% of the power piston""s stroke towards the cylinder head, and ends at about 15% of downward travel of the power piston""s expansion stroke. Means are provided for the introduction of heat into the cylinder. The engine can be operated with almost complete expansion of the charge.
(a) The engine compresses the fluid in the same cylinder that the engine expands the fluid in.
(b) The engine compresses the fluid in a portion of the cylinder that is not heated by the hot gases.
(c) The engine saves the heat from the exhaust gases and releases the heat to the compressed fluid.
(d) All of the engines valves operate at compressor exit temperature or slightly higher.
(e) The engine exhausts most of the exhaust gases each stroke.
(f) The engine can be operated so that the charge is almost fully expanded.